Detection of chemical vapor deposition grown diamond

ABSTRACT

Diamonds may be identified as grown by the use of chemical vapor deposition. One or more diamonds may be placed on a surface and exposed to short wavelength light. Diamonds that fluoresce red may be identified as grown by the use of chemical vapor deposition. In some embodiments, the diamonds are cooled prior to exposure to the short wavelength light.

CLAIM OF PRIORITY

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 to Robert C. Linares et al., U.S. patentapplication Ser. No. 12/463,152, entitled “DETECTION OF CHEMICAL VAPORDEPOSITION GROWN DIAMOND,” filed on May 8, 2009, which claims thebenefit of priority under 35 U.S.C. §119(e) to U.S. Provisional PatentApplication Ser. No. 61/051,854, filed on May 9, 2008, the benefit ofpriority of each of which is claimed hereby, and each of which areincorporated by reference herein in its entirety.

BACKGROUND

Chemical vapor deposition (CVD) grown diamonds can be difficult todistinguish from mined diamonds using conventional techniques. Detectionof CVD diamond is of importance to the diamond industry to prevent thefraudulent sale of CVD diamond as natural diamond, and to enable thedetection of CVD diamond for the purpose of ensuring that there is nomisrepresenting natural as CVD diamond. Further, the detection of CVDdiamond may be useful for protecting intellectual property rights.

The detection of CVD diamond is difficult and laborious due to the factthat multiple instruments are needed. Such instruments are used to firstdetermine that the diamond in question is a type II A. Colorless cvddiamonds currently are type II A which indicates a very low nitrogenlevel. The instruments are then used for testing for the presence of N-Vcenters, which are a substitutional nitrogen atom adjacent to a carbonvacancy. Finally, instruments are used to microscopically view diamondsfor features such as strain. All of these tests are required to raisethe certainty that a diamond is natural or cvd. None of these tests arecomplete in themselves, as the presence of N-V centers is rare innatural diamonds, but does occur. Such N-V centers fluoresce atred-orange wavelengths due to it's two main emission peaks centered at575 and 637 nm. The purer the diamond the weaker the fluorescence. Thefluorescence can also be seen by illuminating the diamond with shortwavelength ultraviolet light in an expensive instrument such as the“Diamond View”. The detection process is long and difficult for largepure stones and nearly impossible for small stones.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block system diagram illustrating detection of chemicalvapor deposition grown diamonds according to an example embodiment.

FIG. 2 is a flow chart of a method of detecting chemical vapordeposition grown diamonds according to an example embodiment.

FIG. 3 is a graph illustrating photo luminescence of CVD formed pink,white and brown diamonds.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which is shown by way ofillustration specific embodiments which may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical andelectrical changes may be made without departing from the scope of thepresent invention. The following description of example embodiments is,therefore, not to be taken in a limited sense, and the scope of thepresent invention is defined by the appended claims.

In one embodiment, a number of cut or uncut diamonds 105 may placed on aplatform or a moving belt 110 as illustrated in a system block diagramat 100 in FIG. 1. The entire content of diamond 105 is subjected toshort wavelength illumination at a light source 120. In one embodiment,a laser of suitable wavelength may be used as the light source 120.Examples of suitable laser sources include commercially available laserdiodes which emit light at wavelengths of 405 nm or 532 nm. Many otherwavelengths may be used that cause fluorescence of diamonds with N-Vcenters, such as wavelengths in the 400 to 550 nm range, and may includeportions of the UV range of 10 to 400 nm, or at least the upper portionsof the UV range. Other sources that provide suitable wavelength lightmay also be used.

The CVD diamonds will fluoresce red-orange and may be picked out by handor by a pick and place robot 130 which is guided to either thefluorescent diamond or the non fluorescent diamond. Alternately, thediamond may be cooled below room temperature as indicated at 140 such asby liquid nitrogen (which greatly increases the brightness of thefluorescence) or some other suitable coolant or thermoelectric cooler.In one embodiment, the diamonds to be tested may be colorless and nearcolorless. In further embodiments, diamonds of different colors, such asyellow, blue, pink, orange, brown, or other color may be tested.

In this manner, large numbers of diamonds may be inspected to separatethe CVD from the natural diamonds. In the event it is desirable todetect and remove diamonds formed by high pressure, high temperaturemethods, or heat treated natural diamonds, different wavelength filterscan be employed in the system to detect these materials by theirfluorescence, and such detected materials may be removed by an operatoror robotic arm.

FIG. 2 is a flowchart of a method for sorting natural diamonds fromdiamonds formed using chemical vapor deposition. At 210, one or morediamonds are cooled below room temperature. The use of liquid nitrogenis one option for cooling, and may be used to cool the diamonds wellbelow room temperature, and in some embodiments, close to thetemperature of the liquid nitrogen if desired. At 220, the cooleddiamonds are exposed to the short wave length light or radiation. Theterm short wave length encompasses short visible light in the blue toviolet range and at least part of the UV spectrum in one embodiment. Inone embodiment, a conveyor belt may be used, and should be run fastenough to ensure that the temperature of the diamonds does not increasesignificantly from their cooled state. At 230, diamonds that fluorescered-orange (approximately 780 nm to 585 nm wavelength) may beidentified. This may be done by human observation, or by imagerecognition software and hardware in some embodiments. Thus, a humanperceivable attribute, the color of the fluorescence may be used toidentify diamonds that are most likely made by CVD processes, withoutthe need for a spectrometer.

At 240, the diamonds may be sorted based on such observation orrecognition, either by hand or by some mechanized device. Puffer typedevices may be used to blow selected diamonds, either natural or CVDgrown diamonds from the conveyor belt as the diamonds move past thepuffer or blower. The puffer or blower may be controlled via input fromthe image recognition software. Diamonds could also be selectivelyremoved using a vacuum pick up tool. The combination of imaging hardwareand software along with an automated (robotic) picking tool, andintegrating software would allow a fully automated system whichidentifies and removes the diamonds with red-orange light emission. Insuch embodiments, the diamonds should be spaced on the conveyersufficiently to allow the puffer or blower or vacuum pick up tool toselectively remove the diamonds. The process may also be run with humaninteraction, such as by dipping a quantity of diamond in the liquidnitrogen, spreading them out on a surface, exposing them to the shortwavelength light, and picking out the diamonds with a tool by hand. Theuse of the tool is desired if the diamonds are still at temperatureswhich could damage skin by contact with the diamonds. In furtherembodiments, suitable shielding may be provided to protect the operatorfrom harmful UV light.

Some natural diamonds may also have N-V centers that cause fluorescencein response to illumination. It currently appears that such naturaldiamonds are very rare. The fact that a natural stone has an N-V centeror centers may result in a natural stone being classified as a diamondmanufactured by CVD methods. In CVD stones, one of the peaks offluorescence may be a doublet, whereas in natural minded diamond stones,single peaks may be observed. If there is reason to suspect that anatural stone has been mistakenly identified as manufactured, it may besubjected to a higher resolution spectrometer to detect the nature ofthe peak or peaks. If only single peaks are observed, the diamond may bereclassified as natural. These checks may be performed as part of sort240 in some embodiments.

FIG. 3 is a graph illustrating photo luminescence of CVD formed pink,white and brown diamonds. The same or similar wavelengths can be foundusing the short ultraviolet and laser light shown above.

The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow thereader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

What is claimed is:
 1. A method comprising: placing multiple diamonds ona surface; cooling the diamonds below room temperature; exposing thediamonds to light having a wavelength at or below 550 nm; andidentifying diamonds that fluoresce between approximately 780 nm to 585nm.
 2. The method of claim 1 wherein the diamonds are cooled by exposingthem to liquid nitrogen.
 3. The method of claim 2 wherein the cooleddiamonds fluoresce at a higher wavelength than uncooled diamonds.
 4. Themethod of claim 1 wherein the surface comprises a conveyor belt.
 5. Themethod of claim 1 wherein the diamonds are cooled by a thermoelectriccooler.
 6. The method of claim 1 and further comprising: removing theidentified diamonds from the surface; subjecting the removed diamonds toa spectrometer to detect one or more peaks; and classifying diamondshaving single peaks as natural diamonds and diamonds having doubletpeaks as chemical vapor deposition formed diamonds.
 7. A methodcomprising: placing multiple diamonds on a surface; cooling the diamondsbelow room temperature; exposing the diamonds to light having awavelength at or below 550 nm; and sorting the diamonds as a functionfluorescence between approximately 780 nm to 585 nm.
 8. The method ofclaim 1 and further comprising cooling the diamonds below roomtemperature prior to exposing the diamonds to light.
 9. The method ofclaim 8 wherein the diamonds are cooled by exposing them to liquidnitrogen.
 10. The method of claim 8 wherein the diamonds are cooled by athermoelectric cooler.
 11. The method of claim 7 wherein the surfacecomprises a conveyor belt.
 12. A method comprising: placing multiplediamonds on a surface; cooling the diamonds significantly below roomtemperature; exposing the diamonds to light having a wavelength at orbelow 550 nm; identifying diamonds that fluoresce between approximately780 nm to 585 nm as diamonds manufactured using chemical vapordeposition; and using a spectrometer to detect doublet emissions whenthe diamonds are exposed to short wavelength light to confirm thatdiamonds that fluoresce are manufactured.
 13. The method of claim 12wherein the diamonds are cooled by exposing them to liquid nitrogen. 14.The method of claim 12 wherein the diamonds are cooled by athermoelectric cooler.
 15. The method of claim 14 wherein the surfacecomprises a conveyor belt.
 16. The method of claim 15 wherein diamondsare removed from the conveyor belt as a function of their detectedfluorescence.
 17. The method of claim 16 wherein the diamonds areremoved by a puffer or vacuum picker.
 18. The method of claim 12 whereinthe diamonds are colorless to near colorless.
 19. The method of claim 12wherein the short wavelength light includes light in the visible to UVrange.
 20. The method of claim 12 wherein the short wavelength lightincludes light in the blue to violet range.